Radio broadcast selecting and distributing system



July 5,1921.

5. E. CLEMENT Filed Feb- 29- 1924 awumto a r W 31 3o 1|... $3 5 0L NEW B .N Q SQQ M w J u PL 33% Patented July 5, 1927.

UNITED STATES Examini- PATENT OFFICE.

EDWARD E. CLEMENT, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO EDWARD F. COLLADAY, OF WASHINGTON, DISTRICT OF COLUMBIA.

RADIO BROADCAST SELECTING AND DISTRIBUTING SYSTEM.

Application filed February 29, 1924. Serial No. 695,992.

My invention relates to systems of radio broadcast distribution, and has for its object the centralization of long range and high selective receiving apparatus, and rendering the same available for the use of subscribers with simple apparatus at their substations.

I attain my object by providing a superheterodyne system of receiving at a central station, preferably including radio frequency amplification for the beat waves, connecting the output side of the system to suitable terminals whereby the same may be connected to any one of a plurality of subscribers lines at will, the connection including suitable rectifying and detecting apparatus whereby it will be unnecessary to place a detector tube at the subscribers station. I find in practice that by connecting the plate circuit of the central oflice detector directly to line, the subscribers receiver Wlll respond to the audio modulations, the reason being apparently two-fold, viz: first, that the current transmitted to the subscribers station is a pulsating asymmetric current,

' and second, that the subscribers line being a twisted pair according to modern telephone practice, furnishes ample capacity for a bypass for radio frequencies.

My invention is illustrated in the accompanying drawing in which the figure is a diagram illustrating one form of my invention.

Referring to the drawing, O is the central station and S is the subscribers station. It

' should be remarked that the lower portion of the figure, including jacks J, the line conductors 24 and 25, and the subscribers station S should extend out to the right of the cord circuit shown at C in the upper part of the figure. In the central station, 1 is an antenna circuit containing variocoupler, 2, a tuning condenser 3. The secondary of the variocoupler is connected in a tuned circuit 4: containing also the secondary of coupler 5, whose primary is connected to an oscillator O. This oscillator comprises as its essential elements the audion tube T, the coils 5 and 5 a tuning condenser 5, and suitable terminals for battery and for the output to the receiving circuit 4. From the tuned circuit 4, wires are connected to the grid and filament of the first detector D, whose plate circuit is coupled to the grid circuit of the amplifier tube A, whose plate circuit in turn is coupled to the grid circuit of a second amplifier tube A, whose plate circuit in turn is coupled to the output terminals 6, which in turn are connected to a spring ack J. Cooperating with this spring jack is a plug P, forming one terminal of a cord circuit 7, 8, 9, 10, whose other terminal is a plug P adapted to cooperate with the spring jacks J of the subscribers lines 2 l25. The cord circuit contains a second detector tube D, whose grid circuit is connected in the usual way to the input or plug terminal P, whose late circuit is connected to the output or p ug terminals P. Interposed in the plate circuit, is a key K, which when operated opens the wire 10 and in cludes operators telephone receiver R therem,

It is assumed that therewill be as many heterodyning sets as are necessary to render available to the local subscribers all desired stations. Each set is su posed to be tuned and available through 511s spring jack J for selection by an operator or operators and connection to one or more subscribers lines through plug and cord circuits PP'. It will be observed that double selection is possible, viz: selection of the particular station wanted by selecting the particular het erodyne set that is tuned for that station, and second, selection of the subscriber to Whom the set is to be connected. By means of multiple jacks subscribers may be connected to one heterodyne set as desired, and it will be noted that the output side of this set is from the radio amplifier terminals, and not from a detector, and that at this stage the volume of current modulated may be built up by interposing banks of amplifiers similar to A or in parallel and if desired by using power tubes. It may readily happen, when some special feature is announced, such as a presidential speech, that many subscribers will desire access to the same distant station. In such case provision must be made for increasing the amperage of amplified current, which can be done in the manner indicated. It will be further observed that the output terminals 6 are connected to bus wires 6 and 6 and across these bus wires may be as many switching terminals as required.

The detector D and its cord circuit as shown are individual to one line at a time,

while connected thereto, and not only are voltage and amperage conditions thus properly met, but the distribution of the detectors among the several connecting circuits, and their interchangeability render it possible to maintain perfect continuity of service without interruption due to burning out or breaking of tubes, which would occur if the detector tubes were permanently associated with either the main receiver or the subscribers line.

In operation the subscriber can call the operator in the usual manner by means of his line signal, not shown, on the telephone switchboard Sw, or by suitable means can set a special signal on the radio switchboard. Flashing his line lamp may indicate radio connection, and the radio operator may be provided with ordinary cords and plugs or equivalent devices to obtain the number 01' letter of the station wanted. Assuming this to be the station to which the antenna circuit l is tuned, the operator then inserts the plug P of an idle cord circuit in the jack J, and the corresponding plug P in the jack J of the calling line, whereupon tuned modulated beat waves from the output terminals 6 will be repeated as modulated pulsating waves in the plate circuit 910. and the subscribers circuit 24 25. These asymmetric -modulated pulsating waves of standard super-audio frequency are receivable in the subscribers headphone H of usual type, or any other equivalent suitable receiver. I findit possible to receive these modulated pulsating waves, even on short wave lengths, for example, 400 to 500 meters, in an ordinary low wound telephone receiver, but much better reception is afforded by using the usual radio telephone receiver, wound to resistance of from 2,000 to 8,000 ohms. The operator may supervise the transmission by means of her key K,

which when closed includes her headphone R in series in the plate circuit 9, P, 24, H, 25, P, 10. I have also found by experiment that it is possible for the operator and the subscriber to converse over the plate circuit, using their magnetic telephones both as transmitters and as receivers. It is even possible to do this without removing the telephone receivers from the ears. Special transmitters may be provided if desired, but if battery transmitters are employed, it will be preferable to include secondary windings of induction coils in the plate circuit or line with the transmitters in the primary circuits. It is possible to accomplish a number of results in this case because of the direct pulsating character of the plate cur- I rent, 50 as to bring the system into closer accord with standard telephone practice, these being impossible with ordinary radio transmission.

To prevent any possible short circuiting of the super audio modulated current at the subscribers station by the ordinary telephone when in use, I may include a radio choke coil To in the telephone branch. The resistance of the radio telephone receiver is usually high enough to prevent its short circuiting voice currents on the line, and the late circuit at central is of course much iigher.

I claim:

l. A system of radio broadcast distribution comprising a central station and subscribers stations served therefrom, with wired circuits interconnecting them, a radio receiver at the central station and frequency transforming means connected therewith, adapted to receive an input of modulated radio waves at relatively high variable frequencies, and to furnish at the output terminals similarly modulated radio waves of standard relatively low but super-audio frequency, means for connecting said receiving apparatus selectively to subscribers lines, and a detector included in said connecting means with its plate circuit terminals connected directly to line.

2. A system of radio broadcast distribution comprising a central station and subscribers stations served therefrom, with minals similarly modulated radio waves ofv standard relatively low but super-audio frequency, means for connecting said receiving apparatus selectively to subscribers lines, a detector tube included in said connecting means so that its grid circuit will receive modulated radio waves and its plate circuit will propagate directly into the connected line similarly modulated unidirectional high frequency pulsating current capable of operating a receiver.

3. A system of radio broadcast distribution comprising a central station and subscribers stations served therefrom, with wired circuits interconnecting them, a radio receiver at the central station and frequency transforming means connected therewith, adapted to receive an input of modulated radio waves at relatively high frequencies, and to furnish at the output terminals similarly modulated radio waves of standard relatively low but super-audio frequency, means for connecting said receiving apparatus selectively to subscribers lines, said means including a pair of switching terminals with a tube detector connected between them, the grid circuit going to the receiving apparatus terminal and the plate circuit directly to the line connected terminal, and receiving means at each subscribers station adapted to respond to modulations carried by the hi h frequency pulsating carrier current in t e plate circuit.

4. A system of radio broadcast distribution comprising a central station and subscribers stations served thereby, with wired circuits interconnecting them, a radio receiving and frequency transforming apparatus at the central station, adapted to receive modulated high frequency radio waves on its input side, and to deliver similarly modulated relatively low standard frequency waves on its output side, bus conductors for the output terminals, switching terminals connected to said bus conductors, switching terminals for the subscribers lines, and connecting means including a detector, adapted to interconnect said bus terminals with said line terminals, and being interchangeable with respect to any of said terminals, said detector being so connected that its plate circuit will always go directly to line.

5. A system of radio broadcast distribution comprising a central station and subscribers stations served thereby, with wired circuits interconnecting them, a radio receiving and frequency transforming apparatus at the central station, adapted to receive modulated high frequency radio waves on its input side, and to deliver similarly modulated relatively low standard frequency waves on its output side, bus conductors for the output terminals, switching terminals connected to said bus conductors, switching terminals for the line circuits, and a plurality of connecting circuits with switching terminals ada ted to cooperate with said bus terminals an said line terminals respectively, each of said connecting circuits including a detector, and all of said connecting circuits being interchangeable, said detector being so connected that its plate circuit will always go directlg to line.

6. A system 0 radio broadcast distribution, a central station and a plurality of subscribers stations served thereby, with wired circuit-s interconnecting them, a plurality of receiving apparatuses at the central station, each tuned to receive on a particular wave length modulated waves from a particular station, and all adapted to deliver at their output terminals the different modulations on a common frequency relatively low standard frequency carrier wave, and each having output terminals connected to switching terminals, switching terminals for the subscribers lines, and connecting means containing a detector with its plate circuit connected directly to the line switching terminal adapted to interconnect any line with any desired receiving apparatus at the central station, together with means at each subscribers station responsive to modulations on the carrier current transmitted over his line.

branches arranged to amplify in the direc- 7. A system of radio broadcast distribution, a central station and a plurality of subscribers stations served thereby, with wired circuits interconnecting them, a plurality of recelving apparatuses at the central station, each tuned to receive on a particular wave length from a particular station, and all adapted to deliver at their output terminals at the same relatively low standard frequency, and each having output terminals connected to switching terminals, switching terminals for the subscribers lines, and connecting means including detector tubes, each having its plate circuit directly connected to the line switching terminal, adapted to interconnect any line with any desired receiving apparatus at the central station, together with means at each subscribers station responsive to modulations on the carrier current transmitted over his line.

8. A system of broadcast distribution comprising a central station and subscribers substations with line circuits interconnecting them, a source of electrical signal waves at said central station, branch connections from said source to a plurality of said lines in common and a unidirectional electrical valve connected in each of said branches, one valve to each line, with its output terminals directly connected to line.

9. A system of broadcast distribution comprising a central station and subscribers substations with line circuit-s interconnecting them, a source of electrical signal waves at said central station, branch connections from said source to a plurality of said lines in common, there being one branch connection for each line and a thermionic tube connected in each of said branches with its plate circuit directly to line.

10. A system of broadcast distribution comprising a central station and subscribers substations with line circuits interconnecting them, a source of electrical signal waves at said central station, branch connections from said source to a plurality of said lines in common, one branch to each line, and amplifying means connected in each of said tion of the line, and with its output termi nal directly connected to line.

11. In a combined telephone exchange and broadcast system having a central station and subscribers stations with wire line circuits interconnect-ing them, a source of electrical signal waves at the central station for broadcast distribution, and a thermionic tube individual to each line arranged to be connected between the said broadcast source and its associated line with its plate circuit 125 directly to line.

In testimony whereof I hereunto afiix my signature.

EDWARD E. CLEMENT. 

